The dissemination of sensors is key to realizing a sustainable, ‘intelligent’ world, where everyday objects and environments are equipped with sensing capabilities to advance the sustainability and quality of our lives—e.g. via smart homes, smart cities, smart healthcare, smart logistics, Industry 4.0, and precision agriculture. The realization of the full potential of these applications critically depends on the availability of easy-to-make, low-cost sensor technologies. Sensors based on printable electronic materials offer the ideal platform: they can be fabricated through simple methods (e.g. printing and coating) and are compatible with high-throughput roll-to-roll processing. Moreover, printable electronic materials often allow the fabrication of sensors on flexible/stretchable/biodegradable substrates, thereby enabling the deployment of sensors in unconventional settings. Fulfilling the promise of printable electronic materials for sensing will require materials and device innovations to enhance their ability to transduce external stimuli—light, ionizing radiation, pressure, strain, force, temperature, gas, vapours, humidity, and other chemical and biological analytes. This Roadmap brings together the viewpoints of experts in various printable sensing materials—and devices thereof—to provide insights into the status and outlook of the field. Alongside recent materials and device innovations, the roadmap discusses the key outstanding challenges pertaining to each printable sensing technology. Finally, the Roadmap points to promising directions to overcome these challenges and thus enable ubiquitous sensing for a sustainable, ‘intelligent’ world.

Flexible, printed and skin-mounted sensors are increasingly used to support long-term monitoring of vital signs. One challenge in printing on-skin devices is in identifying substrates which both match the properties of the epidermis and can tolerate the temperatures required to cure ink. This work describes a method for screen printing on polyurethane (PU) films using a paper ‘carrier’ during the curing process. We printed Ag/AgCI on $\mathbf{Tegaderm}^{\mathbf{TM}}$ film (3M), demonstrating that carrier bound prints do not shrink or lose conductivity when exposed to temperatures as high as $220\ ^{\circ}\mathrm{C}$ . We also printed capacitive electrocardiography sensors on Tegaderm, where the electrode connects to the skin with a layer of adhesive which acts as a dielectric. These probes were able to acquire signals with discernible waveform features (P-Q-R-S-T), exhibiting an signal-to-noise ratio of 32.8 dB and a skin-contact impedance at 30 Hz of 648 $\pm 278\Omega$ (standard deviation).

Advances in flexible electronic materials have seen the emergence of ultra-thin epidermal sensors for monitoring human electrocardiography (ECG), with some designs only micrometers in thickness. Application of this technology to mice could refine current pre-clinical protocols by enabling more humane, non-invasive monitoring systems. This work characterises the electrical properties and skin-conformity of three screen printed Ag/AgCl ECG electrode designs for mice. Specifically, we examine substrates of temporary tattoo paper and 25 µm thick polyester, which attach to the skin using conductive paste or a polyurethane-film (PU). This work demonstrates how skin-conforming sensors can collect acceptable quality mouse ECG signals. Whilst electrical characterisation suggests that probes without conductive paste are reliant on capacitive coupling, where interface adhesives and the mouse’s thin stratium corneum act as a dielectric. Finally we examine skin conformity with histological imaging, revealing tattoo substrate and PU to be considerably more compliant than polyester. This opens up discussion into which materials would be most suitable in developing an ECG interface for free-moving mice.

Oesophageal stents are meshed tubular implants designed to maintain patency of the oesophageal lumen and attenuate the symptoms of oesophageal cancer. Oesophageal cancers account for one in twenty cancer diagnoses and can lead to dysphasia, malnutrition and the diminishment of patient quality of life (QOL). Self-expanding oesophageal stents are the most common approach to attenuate these symptoms. Recent advances in oncological therapy have enabled patient survival beyond the lifetime of current devices. This introduces new complications for palliation, driving the need for innovation in stent design. This review identifies the factors responsible for stent failure. It explores the challenges of enhancing the longevity of stent therapies and outlines solutions to improving clinical outcomes. Discussions focus on the role of stent materials, construction methods, and coatings upon device performance. We found three key stent enhancement strategies currently used; material surface treatments, anti-migratory modifications, and biodegradable skeletons. Furthermore, radioactive and drug eluting stent designs were identified as emerging novel treatments. In conclusion, the review offers an overview of remaining key challenges in oesophageal stent design and potential solutions. It is clear that further research is needed to improve the clinical outcome of stents and patient QOL.